Amalgams or alloys of metal powders composed mainly of silver and mercury, have long been used as dental filling materials. However, various dental filling materials have recently been studied and developed for the purpose of preventing such environmental pollution. Due to the fact that such amalgams have high strength, assure easy manipulation during treatments, and are harmless in the mouth, their usefulness is being reconsidered. However, mercury is essentially a harmful substance to which severe environmental standards are applied. Due to its unique properties, mercury metal poses a severe pollution threat. To prevent such pollution, it is preferred that scattered mercury particles, etc. be contained in a specific place or a closed system for collection. Following such an idea, a mercury pollution-preventing apparatus has been developed and used, wherein the preparation of amalgams can be carried out in such a manner that environmental pollution due to mercury is reduced. For instance, an apparatus is known which contains an amalgam-preparing chamber having therein a space defined on a plate base having a number of small openings by the walls, wherein one of them is at least transparent and includes a openable door, the space being designed to receive an amalgam-preparing device, a funnel attached at the top to the lower end of such chamber in a closed state and without any gap therebetween, a vertically movable water tank into which a funnel pipe extending from the central bottom of said funnel is inserted, a mercury vapor-capturing bin filled with an absorbent composed of wool, etc. or activated charcoal, and an electrically driven pump.
With the aforesaid apparatus, however, it is very difficult to determine when the activated charcoal or absorbent is used up. Misjudgment of replacement time leads to environmental pollution due to mercury. On the contrary, frequent replacement results in waste of material and hence a rise in the processing cost. In addition, the mercury vapor-capturing power is rather low. Since all the scattered mercury, amalgam pieces and mercury vapor generated in the amalgam-preparing chamber are allowed to pass through the fine funnel pipe, there is an increase in the flow rate of nongaseous mercury such as fine mercury particles or amalgam particles. Hence, the nongaseous mercury in the gas stream is captured in water by passing it through the water tank, but it is, in most cases, impossible to prevent a portion of these fine particles from reaching the bin. As a result, the service life of the absorbent or activated charcoal is not only reduced, but the amount of nongaseous mercury captured in the bin such as fine mercury particles varies from time to time and from place to place. This results in further misjudgment of replacement time.